Oscillators – With frequency adjusting means – With voltage sensitive capacitor
Reexamination Certificate
1999-07-02
2001-03-06
Pascal, Robert (Department: 2817)
Oscillators
With frequency adjusting means
With voltage sensitive capacitor
C331S167000
Reexamination Certificate
active
06198360
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to oscillators generally and, more particularly, to a quadrature current frequency modulation oscillator.
BACKGROUND OF THE INVENTION
Oscillators are used in a variety of design applications. One type of oscillator is a inductor/capacitor (LC) oscillator. In the case of an LC oscillator, one conventional method used to change the frequency of the oscillator is to implement a variable junction capacitor to change the resonant frequency of the LC circuit.
A disadvantage with adjusting the frequency of LC oscillators using variable junction capacitors to change the resonant frequency is the accuracy problems introduced when fabricating variable junction capacitors. Furthermore, low loss junction capacitances may not be convenient to fabricate in every process technology. The modulation is non-linear over the limited range that can be achieved.
Another type of oscillator is a ring oscillator. In the case of a ring oscillator, one conventional method used to change the frequency of the modulation of the oscillator is to vary the internal delay of the oscillator. Adjusting, either the resistance (R) or the capacitance (C) of the gain stages varies the delay. Another approach to varying the delay is to implement two delay paths and to change the proportion of the signal through the two different paths.
A disadvantage with the use of ring oscillators may occur when built using processes, that has a relatively high variation of parameters due to variations in processing. As result, such oscillators may require large modulation ranges to compensate for such process variations.
Another type of oscillator is an integrated relaxation oscillator. Integrated relaxation oscillators are not widely used because of the need to either (i) provide accurate absolute value resistors or absolute value charging currents. Integrated relaxation oscillators may be susceptible to undesirable amounts of phase noise.
SUMMARY OF THE INVENTION
The present invention concerns a circuit and method used in LC or ring oscillators. The present invention may modulate the frequency of oscillation by detecting a quadrature signal and controlling the sign and magnitude of the quadrature signal that may be feedback to the oscillator to cause the oscillator to run either faster or slower (dependent on the sign of the quadrature signal) than the unmodulated oscillator.
In one example, the quadrature currents in the reactive components are sensed across one or more series resistors. These quadrature voltages are feedback through complementary differential gain (e.g., g
m
) amplifiers, whose differential gain gm is controlled by the modulation voltage or differential amplifiers whose gains are controlled by the modulation voltage and their outputs are summed to vary the magnitude and phase of the quadrature modulation current.
The objects, features and advantages of the present invention include providing an LC oscillator that (i) is relatively stable, (ii) reduces sensitivity to process variations, (iii) has a low phase noise, (iv) uses a reduced or minimum amount of power, (v) has a relative stable modulation sensitivity over temperature and process variations, and/or (vi) has a linear relationship between the modulation voltage and the frequency.
REFERENCES:
patent: 4061987 (1977-12-01), Nagahama
patent: 4492934 (1985-01-01), Sugimoto
patent: 4588968 (1986-05-01), Wile
patent: 5418497 (1995-05-01), Martin
Choe Henry
Cypress Semiconductor Corp.
Maiorana P.C. Christopher P.
Pascal Robert
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